Axial piston rotary barrel type hydraulic pumps or motors

ABSTRACT

The invention obviates distortion in the cylinder liners of axial piston pump/motors by flooding a space around the liners with working fluid derived from the pump/motor ports, so that the liners are subject to equal internal and external pressures.

United States Patent 1 Clerk 1 AXIAL PISTON ROTARY BARREL TYPE HYDRAULICPUMPS OR MOTORS June 17, 1975 2,518,787 8/1950 Huhtala 92/164 2,678,2475/1954 Geyer 92/169 2.815.718 12/1957 Avery 91/498 3,169.488 2/1965Galliger i. 91/507 3,656.407 4/1972 Hause 91/494 Primary ExaminerWilliamL. Freeh Attorney, Agent, or Firm-Imirie, Smiley & Linn [57] ABSTRACTThe invention obviates distortion in the cylinder liners of axial pistonpump/motors by flooding a space around the liners with working fluidderived from the pump/motor ports, so that the liners are subject toequal internal and external pressures.

4 Claims, 2 Drawing Figures [76] Inventor: Robert Cecil Clerk, EdisonHouse,

Fullerton Rd., Glenrothes, Fife, Scotland [22] Filed: June 15, 1973 [21]App]. No.: 370,345

[52] US. Cl. 91/499 [51] Int. Cl. F0lb 13/04 [58] Field of Search91/499, 507, 498; 92/169, 92/164 [56] References Cited UNlTED STATESPATENTS 2,487,920 11/1949 Celenza 92/169 fi f PATENTEDJUK 17 I975 SHEETFIG.|

AXIAL PISTON ROTARY BARREL TYPE HYDRAULIC PUMPS OR MOTORS BACKGROUND OFTHE INVENTION This invention relates to axial piston rotary barrel typehydraulic pumps or motors with means for reducing strain in the cylinderwalls.

In high pressure hydraulic pumps and motors. and in particular axialpiston configurations, the assembled running clearance of the pistons inthe cylinders is partly determined by the anticipated strain distortionof the cylinders under pressure as it affects the circularity and linearalignment of the cylinder bores. However. this same strain at the sametime increases the diametral running clearance of the cylinder over thepiston, and as the leakage slip past the piston is a cube function ofthe clearance and a linear function of the pressure, the tendency tohigh leakage at high pressure is usually met by increasing the length ofthe leakage path, i.e.. the length of the piston, in spite of thiscausing greater susceptibility to the effects of cylinder distortion notto mention increasing the mass and inertia of the piston and itsfrictional surface area.

It is well known to form the cylinder bores by inserting pre-honedsleeves into the barrel. but care is usually exerted in ensuring thatthe sleeves fit snugly in the bores of the barrel so as to transfer thepressure stress to and share the strain with the barrel material, thepressure fluid being excluded from this area to obviate creep leakagebetween sleeve and barrel. In other engineering applications wet-liners"are quite common. but the fluid in the space within a cylinder blockbore external of the sleeve is not the pressure working fluid butusually a coolant.

SUMMARY OF THE INVENTION The object of the present invention is toprovide a form of cylinder within a barrel which is not susceptible inany marked degree to the pressure of the working fluid and theconcomitant strain effects in the main operating area of the pistonwithin the cylinder, so that the working clearance of the piston withinthe cylinder can be a constant regardless of pressure, and the length ofthe piston can be minimised to permit a precisely de' fined leakagevarying only with working pressure by the linear function.

A further object is to enable lower production and assembly costs to beachieved and to allow a wider choice in the material specification ofthe barrel. as the strain modulus will be less critical.

According to the invention I provide an axial piston rotary barrel typehydraulic pump or motor having a cylinder barrrel including a pluralityof substantially axially aligned cylinder bores each of which is fittedwith a cylinder liner sealed at its ends to that bore to provide anannular space between the inner wall of the bore and the outer wallofthe liner, and channels connecting the annular spaces to the cylinderports so that the spaces are flooded with an subject to the pressure ofthe working fluid.

Preferably the radial widths of the annular spaces towards the port endsof the bores are made greater than at the remote ends. and this can beachieved either by reducing the thickness of the liners or by enlargingthe bore diameters.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a central vertical sectionthrough a cylindri cal barrel showing one cylinder and liner in detail,and

FIG. 2 is a central vertical section through an alternative form ofcylinder and liner.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. 1, thecylinder barrel 1 is provided with a plurality of oversize,substantially axial bores which receive liners 2.

The liners are inserted from the bottom of the barrel and are sealed tothe bores by O-rings 3 and 4 and are kept in place by a star plate 5.

A narrowing of free the section of the liners towards their upper endsprovides an enlargement of the volume of annular chambers 6 formedbetween them and the cylinder barrel 1.

Channels 7 connect the chambers 6 to the cylinder ports 8 whichcommunicate with working fluid transfer ports 12 in a fixed valve block13 so that those chambers are flooded with and pressurised by theworking fluid.

In the alternative form of cylinder shown in FIG. 2 like references areemployed as for FIG. I.

The liner 2 in this case is inserted from the top of the cylinder barrel1 and is sealed to the oversize bore therein by O-rings 3 and 4.

The ring 4 is located between a chamfered keep ring 9 and a shoulder 10formed on the liner 2. while the ring 3 is trapped in a groove formed ina barrel cover plate II, which in fact is extended upwardly in itscentral part to constitute a bearing sleeve (not shown).

As before the annular space 6 is flooded with and pressurised by workingfluid admitted by channels 7 from the port 8.

For certain pump or motor applications the liners are only looselyentrapped by the star plate and are thus able to rotate randomly toequalise the cylinder bore wear due to either high speed centrifuging ofthe piston masses or the driving or driven torque transmitted by thepistons.

I claim:

I. An axial piston rotary barrel type hydraulic pump- /motor having acylinder barrel including a plurality of substantially axially alignedcylinder bores each of which includes a cylinder port in one endcommunicating with a Working fluid transfer port in a stationary valveblock, each of said bores being fitted with a cylinder liner sealed atboth of its ends to said bore, the outer diameter ofsaid liner beingsubstantially less than the inner diameter of said bore, to provide afree annular space between the inner wall of the bore and outer wall ofthe liner. and channels connecting said annular spaces to said cylinderports whereby said annular space is entirely closed except forcommunication with said cylinder port through said channels, so thatsaid spaces are flooded with and subject to the pressure of said workingfluid.

2. A pump/motor according to claim I, in which the radial widths of theannular spaces towards the port ends of the bores are greater than atthe remote ends.

3. A pump/motor according to claim 1 in which *O rings are employed toseal the liners to the cylinder bores.

4. A pump/motor according to claim 1 in which the length of said linersis less than the length of said cylinder bores, so that said liners arefree to rotate in said cylinder bores.

1. An axial piston rotary barrel type hydraulic pump/motor having acylinder barrel including a plurality of substantially axially alignedcylinder bores each of which includes a cylinder port in one endcommunicating with a working fluid transfer port in a stationary valveblock, each of said bores being fitted with a cylinder liner sealed atboth of its ends to said bore, the outer diameter of said liner beingsubstantially less than the inner diameter of said bore, to provide afree annular space between the inner wall of the bore and outer wall ofthe liner, and channels connecting said annular spaces to said cylinderports whereby said annular space is entirely closed except forcommunication with said cylinder port through said channels, so thatsaid spaces are flooded with and subject to the pressure of said workingfluid.
 2. A pump/motor according to claim 1, in which the radial widthsof the annular spaces towards the port ends of the bores are greaterthan at the remote ends.
 3. A pump/motor according to claim 1 in which''''O'''' rings are employed to seal the liners to the cylinder bores.4. A pump/motor according to claim 1 in which the length of said linersis less than the length of said cylinder bores, so that said liners arefree to rotate in said cylinder bores.